some concepts

Official Python bindings with a focus on reinforcement learning and robotics.
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hotgarlic
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Joined: Sun Dec 10, 2017 3:49 pm

some concepts

Post by hotgarlic » Sun Dec 10, 2017 3:56 pm

what is the difference between link and body?
indice and index?
What is the meaning for frame?
On pybullet contex, many concepts may be different to other engine, I am confused.

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Erwin Coumans
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Re: some concepts

Post by Erwin Coumans » Mon Dec 11, 2017 7:23 pm

In robotics and multibodies, bodies are often called a 'link'.
In pybullet, there is the concept of 'bodyUniqueId' for a multibody.

If the multibody has children, those children are called 'links'. You can access all the links of a multibody through a link index, starting from 0 to the number of links. Each link (body) is connected to its parent through a joint, such as a revolute (hinge) joint or prismatic (slider)joint. Since each link has one joint to its parent, the link index == joint index.

This is pretty standard in robotics, and used in pybullet.
The root link/body of a multibody is called 'base'. A base can be either floating (6 degrees of freedom) or fixed (0 degrees of freedom).

For further information, use the PyBullet Quickstart Guide at https://docs.google.com/document/d/10sX ... e70wns7io3

hotgarlic
Posts: 7
Joined: Sun Dec 10, 2017 3:49 pm

Re: some concepts

Post by hotgarlic » Tue Dec 12, 2017 7:53 am

Thanks for your reply @Erwin Coumans
Your explanation is good for me, for I am not clear after reading the guide of pybullet until your reply.

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